Alternating current magnet



July 23, R N E 2,009,188

ALTERNAT ING CURRENT MAGNET Filed Oct. 14, 1933 FIG. FIG. 3.

INVENTOR A! ATTORNEY Patented July 23, 1935 PATENT OFFICE ALTERNATINGCURRENT MAGNET Rufus A. Andrews, Mount Vernon, N. Y., assignor to WardLeonard Electric Company, a corporation of New York Application October14, 1933, Serial No. 693,594

8 Claims. (01. 175-338) This invention relates to alternating currentmagnets wherein a closed circuited path is provided for induced currentsfor the purpose of avoiding so called chattering or mechanical vibrationof the movable part or parts.

The main objects of the improvement are to provide a form ofconstruction and relationship of parts that will be of a simplecharacter, require comparatively low manufacturing costs in material andlabor, occupy small space, and ac-' complish its purpose eflectively andefficiently. Other objects and advantages will be understood from thefollowing description and accompanying drawing.

When an electromagnet is excited by an alternating current, theattractiveforce on the armature varies from zero to a maximum, andreturns to zero, twice during each cycle. Consequently, under theinfluence of any external force, such as a spring or gravity, thearmature will alternately leave and return to the core with a frequencycorresponding to that of the alternating current, resulting in vibrationand considerable noise, or humming. .Thismay be largely overcome by somemeans for maintaining a flux continuously between the armature and core.It is common practice to use a shading coil or lag loop for thispurpose. This loop embraces a portion of the core and has had the formof a single turn of copper, brass or similar-material, inserted in theendot the core. This low resistance closed circuited conductor hasappreciable self-inductance which causes a phase difference between theflux passing to the armature by way of that portion of the cpre embracedby the lag loop and the flux passing to the armature directly throughthat portion of the core not so embraced. Consequently, there is noperiod when there is not a flux between the armature and the core. Thisresults in an attractive force always being exerted between e armatureand the core and reduction of vib tion andnoise.

A conventional practice has been to use a laminated or solid magnet corewith a straight slot completely traversing the core face, adjacent tothe armature, and of such size that one leg of the lag loop may beplaced in it. The core face is thus divided into two sections, thecenters of which are displaced relatively to each other and o to theaxial center line of the core. The force of approximately equal to thecenter to center distance of the two sections. Unless the points ofcontact between the armature and the core are in a plane intersected bythe line of action of both of the above forces of attraction, there willbe resultant forces tending to rock or wabble the armature with aresultant noise of vibration. This rocking or wabbling effect may bereduced somewhat by careful-machining of the core and armature. In somecases two straight slots are cut across-the face of the core and twoopposite sides of a rectangular shaped loop are placed in the two slotswith the ends of the loop extending beyond the core. This gives a moresymmetrical disposition of the fiux but requires careful and costlymachine Work.

These prior forms of magnets are not eflicient or fully satisfactory inaccomplishing their purpose. They are also objectional, not only onaccount of the refined machine work required, but also because thestraight slot or slots for the loop have to be milled in a separatemilling operation after the core is otherwise finished. Furthermore, theportion of the lag loop which extends beyond the core face prevents themagnet coil from being uniformly wound thereover and thus prevents theattainment of a compact form of structure and reduces the eificiency.Again, in some forms of magnets, it is desirable to insert a centrallylocated spring or a movable part and this cannot be done when the lagloop passes across or near the central axis of the core. By the presentinvention these various objections and disadvantages are overcome.

The accompanying drawing illustrates a preferred embodiment of myinvention in a particularly advantageous form of electromagnet for aparticular purpose. Fig. 1 is a vertical central section of acontrolling magnet and associated parts; Fig. 2 is a cross-section ofthe movable element of the magnet on the line A-A of Fig. 1; Fig. 3 is aview similar to Fig. ,1 except that the ring loop is inserted in theface of the fixed core of the magnet, as distinguished from beinginserted in the face of the movable element of the magnet; and Fig. 4 isa cross-section of the fixed core on the line BB of Fig. 3.

Referring to Fig. 1, the parts are embraced and supported by a U-shapedsteel member I and riveted thereto are two spaced transverse steelmembers 2. At the bottom of the inverted U- shaped member I, is fasteneda transverse plate 3 of insulating-material which carries the bindingposts and supports the fixed switch contacts 4. These switch contactsare diametrically opposite each other. A dash pot 5, having a plunger 6,is supported in the upper part of the frame i and spaced from the topcross piece of the frame I. A check valve 5a is located in the end ofthe dash pot for permitting the plunger 6 to move down quickly when adownward force is exerted thereon. A stem or spindle i is secured at itsupper end to the plunger 6. The spindle has an enlarged intermediatecylindrical portion I0 and at its lower end carries a cone 8 of metalwhich is insulated from the spindle by the insulating intermediateportion 9. The cone 8 is adapted to engage the contacts 4 when thespindle is raised to its upper position, as shown in Fig. 1. Acylindrical steel core ii, having a central opening, is riveted, orotherwise secured, to the lower transverse plate 2, the lower end of thecore H extending within a central opening in the plate 2. A bridgingcross plate i4 is riveted at its ends to the lower side of the lowercross plate 2 and has a central opening through which the spindle 1passes. A spiral spring i2 encircles the spindle i and. extends betweenthe enlarged portion ill of the spindle and the bridge plate It. Thisspring, by being supported at its lower end by the bridge plate tends tokeep the spindle i and the dash pot 6 in their upper position and tokeep the switch closed. The coil or winding M of the magnet is locatedbetween the two transverse plates 2 and is wound upon a tube E3 ofinsulating material extending between the central openings of the plates2. The movable element of the magnet is in the form of a cylindricalsteel plunger l5 having a small central opening through which thespindle 7 passes and a larger central opening at its lower end for thereception of the enlarged portion iii of the spindle. In the lower faceof the plunger IS a circular concentric slot is cut for the reception ofthe lag ring I6. This lag ring is shown in the form of a short cylinderand is tightly forced into the slot so as to be firmly and permanentlyheld therein. As shown in Fig. 2, a cylindrical concentric portion ofthe plunger I5 is embraced by the ring l6 and a cylindrical concentricportion of the plunger l5 envelops the outside of the ring l6. The ringis preferably made of copper but may be made of other conductivematerial.

When in the position shown in Fig. I, the cone 8 bridges the contacts 4for the purpose of completing a circuit of some device which is to becontrolled, the spring I! holding the parts in their upper position.When the magnet winding M is energized, the core I5 is magneticallydrawn downwardly until it engages the fixed core II, the plunger 6 ofthe dashpot and the bridging contact 8 being moved downwardly by thecore I 5 and causing the opening of the circuit to be controlled. Aslong as the winding M is excited, the parts will be held in theirdownward-position. When the winding M is de-energized, the spring I!will force the spindle and plunger 1 5 upwardly and cause the dashpotplunger to move against the compression of the air in the dashpot. Aftera certain time element, the bridging switch element 8 will engage thecontacts 4. Thus when the magnet M is excited, the controlled switchwill be opened quickly and held open until the magnet M is de-energized,when after a certain time interval, the switch controlled will again beclosed.

In Figs. 3 and 4, the lag ring l6, instead of being" inserted in theface of the movable element i5, is embedded in the'upper face of thefixed element ii.

It will be appreciated from the foregoing, that by use of a circular lagring located concentric with the axis of the core, any rocking orwabbling effect is avoided because the lagging flux and the fiuxunaffected by the lag' ring are concentric and are uniformly distributedaround the center and maintain an attractive force having the samecenter. Also, owing to the fact that the lag ring has no portionsextending beyond the core, the magnet winding may be formed close to thecore and thus be more emcient. Moreover, by placing the lag ringentirely within the contacting face of the core, the efilciency isincreased because it is entirely surrounded on the inside and outside bythe iron or steel and the leakage flux is reduced to a minimum.

This improved form of construction also permits the center of the coreto be hollow for the reception of a spindle or counteracting spring, orother parts, without interfering with the location of the ring loop. Inthe particular application of this invention already described, it willbe noted that an ample length of the spring i2 is provided so thatwithin the range of movement of the plunger, the tension of the springis not objectionably changed. It will also be noted that by reason of noprojecting parts extending beyond the sides of the plunger or core, theair gap between the same and the cross plates 2 may be made very smallwhich, of course, increases the efiiciency of the magnet. It will alsobe apparent that by making the lag ring concentric with the axis of themovable core, or :with the axis of the fixed core when placed therein,the machining of the cores may be accomplished in the least expensivemanner, as the only machining necessary is to cut a circular slot in oneend of the core at the time the core; is being turned in a lathe to itsproper shape".-*Thus, by means of this invention, I am able to provide amagnet of a highly efficient type, compact in form, of low cost ofmanufacture and efiective in avoiding the ,noise of vibration of themovable element.

Although I have shown my improvement applied to a solenoid form ofmagnet, the invention may be embodied in other forms of magnets and havethe ring loop embedded in the face of either the fixed or movableelement of the magnet; and it will be understood that variousapplications and adaptations of the invention may be made withoutdeparting from the scope thereof.

I claim:

,1. The combination of a magnet winding, a movable cylindrical magneticelement within said winding, said element having a central recess in oneend thereof, a spiral spring having one end seated in said recess formoving said element in one direction, and a closed conducting circularring in the face of said end of said element and concentric with theaxis of said element 2. The combination of a magnet winding, 9;

movable cylindrical magnetic element within said winding, 9. fixedcylindrical magnetic element within said winding, one of said elementshaving a central opening, a spindle passing through said and also havinga central opening, a spindle passing within said openings, a springencircling said spindle for moving said movable element in onedirection, and a closed conducting circular ring in the face of one ofthe adjoining ends of'one of said elements and concentric with the axisthereof.

4. An electromagnet having a cylindrical form of winding and having afixed magnetic element and a movable magnetic element, one of saidelements being cylindrical and extending within said winding, a closedconducting circular ring in the face of the element extending withinsaid winding, said ring being concentric with the axis of the magnet andenveloped by said winding.

5. An electromagnet having a winding and a fixed magnetic element and amovable magnetic element, and a closed conducting circular ring insertedin the face of one of said elements, said ring being continuouslyembraced on its outer side and on its inner side by portions of theelement in which it is inserted.

6. An electromagnet having a winding and a fixed magnetic element and amovable magnetic element, a closed conducting circular ring inserted inthe face of one of said elements and concentric with the axis of themagnet, said ring being continuously embraced on its outer side and onits inner side by portions of the element in which it is inserted.

'Z. An electromagnet having a winding and a fixed magnetic element and amovable magnetic element, one of said elements having a circular slot inits face concentric with the axis of said winding, and a closedconducting circular ring inserted in said slot and being continuouslyembraced on its outer side and on its inner side by the walls of saidslot.

8. An electromagnet having a winding and a fixed magnetic element and amovable magnetic element, one of said elements having a circular slot inits face concentric with the axis of said winding, and a closedconducting circular ring inserted in said slot and being continuouslyembraced on its outer side and on its inner side by the walls of saidslot and being also enveloped by said winding.

RUFUS A. ANDREWS.

